Semiconductor elements may include transistors of various sizes driven at various voltages. Among the various transistors, high-voltage transistors driven at high voltage may require a thick, or relatively thick, gate dielectric layer. Further, in order to prevent punchthrough and strengthen breakdown voltage characteristics, a source/drain of the high-voltage transistor may be formed as an LDD (Lightly Doped Drain) structure or a DDD (Double Doped Drain) structure including a low-concentration impurity region and/or a high-concentration impurity region.
For example, the source/drain of the high-voltage transistor may be formed as a FLDD (Field Drift Lightly Doped Drain) structure or a MLDD (Modified Lightly Doped Drain) structure.